The present invention is directed to novel conformationally restricted polyamines and their use in the selective inhibition of neoplastic cell growth.
Complete bibliographic citations to the references mentioned below are listed in the Bibliography, immediately preceding the claims. All of the references cited below are incorporated herein by reference in their entirety.
It has been known since the 1950""s that conformation is a determinant in the spatial arrangement of functional groups, and that enzymes or drug receptors prefer specific ligand conformations or a specific distribution of conformations. This fruitful concept led to many decisive successes in drug design. A few examples will suffice to illuminate the subject.
The synthesis of conformationally constrained analogs of an inherently conformationally flexible substance such as acetyl choline helped to secure its xe2x80x9cbioactive conformations,xe2x80x9d i.e., those conformers which are active at the muscarinic and nicotinic receptors. The trans-cyclopropyl analog of acetyl choline was shown to be preferred by the muscarinic receptor. Conformationally restricted analogs of dopamine, GABA, glutamic acid, histamine and serotonin have been obtained by introducing rigid rings into their structures. The constrained analogs have valuable chemotherapeutic effects.
The use of conformational restriction has also been very fruitful in the design of bioactive polypeptides. Polypeptides have so many flexible torsion angles that enormous numbers of conformations are possible in solution. The introduction of rings into the linear peptide chains reduces the number of conformations and has allowed the preparation of several biologically active substances. For instance, a cyclic hexapeptide possessing somatostatin activity is known.
Conformationally restricted enkephalin analogs are known, as are bicyclic lactam inhibitors (enalapril and enalaprilat) of the angiotensin converting enzyme.
Similar strategies have recently led to the development of a peptidomimetic benzodiazepine containing at least two conformational restrictions: a bicyclic heterocycle and an acetylene linker. The benzodiazepine is a non-peptide RGD (Arg-Gly-Asp) receptor antagonist.
The concept of conformational restriction led to the discovery that the bioactive conformation of the immunosuppressor cyclosporin A (CsA) only binds to cyclophylin A when the amide bond between the 9-position and 10-position residues in CsA is trans.
However, the prior art is silent regarding biologically active polyamines which are conformationally restricted by the introduction of one or more ring structures into the polyamine skeleton.
The present invention is directed to conformationally restricted polyamines of Formula I:
Exe2x80x94NHxe2x80x94Dxe2x80x94NHxe2x80x94Bxe2x80x94Axe2x80x94Bxe2x80x94NHxe2x80x94Dxe2x80x94NHxe2x80x94Exe2x80x83xe2x80x83(I)
wherein A is selected from the group consisting of C2-C6 alkene and C3-C6 cycloalkyl, cycloalkenyl, and cycloaryl; B is independently selected from the group consisting of a single bond and C1-C6 alkyl and alkenyl; D is independently selected from the group consisting of C1-C6 alkyl and alkenyl, and C3-C6 cycloalkyl, cycloalkenyl, and cycloaryl; E is independently selected from the group consisting of H, C1-C6 alkyl and alkenyl; and pharmaceutically-suitable salts thereof.
The invention is also drawn to a method of synthesizing the Formula I compounds. Here, a compound of Formula II:
HOxe2x80x94Bxe2x80x94Axe2x80x94Bxe2x80x94OHxe2x80x83xe2x80x83(II)
is reacted with with a protecting reagent, preferrably mesitylenesulfonyl chloride, to yield a compound of Formula III:
PROTxe2x80x94Oxe2x80x94Bxe2x80x94Axe2x80x94Bxe2x80x94Oxe2x80x94PROTxe2x80x83xe2x80x83(III)
wherein PROT is the protecting group.
Then, the Formula III compound is reacted with a compound of Formula IV:
Exe2x80x94N(PROT)xe2x80x94Dxe2x80x94NHxe2x80x94PROT)xe2x80x83xe2x80x83(IV)
to yield a compound of Formula V:
Exe2x80x94N(PROT)xe2x80x94Dxe2x80x94N(PROT)xe2x80x94Bxe2x80x94Axe2x80x94Bxe2x80x94N(PROT)xe2x80x94Dxe2x80x94N(PROT)xe2x80x94Exe2x80x83xe2x80x83(V)
It is much preferred that the protecting group, PROT, in both the Formula III intermediate and the Formula IV intermediate be a mesitylenesulfonyl moiety.
The Formula V compound is then deprotected to yield a compound of Formula I.
The present invention is also drawn to pharmaceutical unit dosage forms containing one or more compounds of Formula I as described above in combination with a pharmaceutically-suitable carrier.
The present invention is also drawn to use of these novel conformationally restricted polyamines. These polyamines have utility as potent antineoplastic agents for use in mammals, including humans.
They also have utility as shape-restricted probes for the study of active-site geometry for enzyme and/or DNA interactions. Because the backbone of these molecules is conformationally restricted, they can only assume a very limited number of 3-dimensional shapes. By assessing the binding of these compounds to various enzyme active sites, or the their ability to interact with DNA, insight is gained into the particular spacial geometry required of enzyme agonists, antagonists and DNA binders. Both the compounds per se and their use is novel.
The present invention was inspired by a study of past failures in the use of polyamine compounds as chemotherapeutic agents in the treatment antiproliferative diseases. It is known that the polyamines spermidine and spermine are essential for normal cell growth. Potent antiproliferative agents have been developed which interfere with the biosynthesis of these compounds, thereby preventing cell proliferation. One of these agents, difluoromethylornithine (DFMO), is currently being studied in humans as a chemopreventive.
The therapuetic success of DFMO is, however, significantly marred by cellular uptake of exogenous polyamines via the polyamine transport system. Cellular uptake of polyamines from the extracellular milieu compensates for the endogenous depletion of the cellular polyamine pools due to the effects of DFMO. Since most food is rich in polyamines (e.g., 100 mL of orange juice contains approximately 400 ppm of putrescine, the spermine precursor), the antineoplastic effect of synthetic analogues which act by depleting the endogenous pool of polyamines is greatly diminished.
The present invention introduces a new approach for the use of polyamine analogs as agents for the treatment of cancer. Notably, both spermidine and spermine interact with DNA. These interactions induce structural changes in isolated DNA. Computer modeling and physico-chemical studies indicate that spermine induces conformational changes in defined DNA sequences. The presently described analogs of natural polyamines may interact with DNA differently than does spermine, resulting in the inhibition of tumor cell growth in culture.
In short, while not being bound to a particular mode of action, the present invention attacks the problem of unchecked cell proliferation by presumably changing DNA conformation via a polyamine analog/DNA interaction. The novel, conformationally restricted polyamines of the present invention display potent anti-proliferative activity.
Consequently, it is the principal aim of the present invention to provide novel, conformationally restricted compounds for use in the treatment of neoplastic cell growth.
These and other aims, objects, and advantages of the present invention will become clear upon a complete reading of the Detailed Description and claims, below.